Array
Array
در جاوااسکریپت یک شیء عمومی است که در ساخت آرایه ها استفاده می شود که اشیائی سطح بالا شبیه فهرست هستند.ساخت یک آرایه
var fruits = ['Apple', 'Banana'];
console.log(fruits.length);
// 2
دسترسی به یک آیتم در آرایه (بر اساس نمایه)
var first = fruits[0];
// Apple
var last = fruits[fruits.length - 1];
// Banana
اجرای حلقه روی آرایه
fruits.forEach(function(item, index, array) {
console.log(item, index);
});
// Apple 0
// Banana 1
اضافه کردن به انتهای آرایه
var newLength = fruits.push('Orange');
// ["Apple", "Banana", "Orange"]
حذف کردن از انتهای آرایه
var last = fruits.pop(); // remove Orange (from the end)
// ["Apple", "Banana"];
حذف کردن از ابتدای آرایه
var first = fruits.shift(); // remove Apple from the front
// ["Banana"];
اضافه کردن به ابتدای آرایه
var newLength = fruits.unshift('Strawberry') // add to the front
// ["Strawberry", "Banana"];
پیدا کردن نمایه یک آیتم در یک آرایه
fruits.push('Mango');
// ["Strawberry", "Banana", "Mango"]
var pos = fruits.indexOf('Banana');
// 1
پاک کردن یک آیتم بر اساس موقعیت نمایه
var removedItem = fruits.splice(pos, 1); // this is how to remove an item
// ["Strawberry", "Mango"]
پاک کردن آیتم ها بر اساس موقعیت نمایه
var vegetables = ['Cabbage', 'Turnip', 'Radish', 'Carrot'];
console.log(vegetables);
// ["Cabbage", "Turnip", "Radish", "Carrot"]
var pos = 1, n = 2;
var removedItems = vegetables.splice(pos, n);
// this is how to remove items, n defines the number of items to be removed,
// from that position(pos) onward to the end of array.
console.log(vegetables);
// ["Cabbage", "Carrot"] (the original array is changed)
console.log(removedItems);
// ["Turnip", "Radish"]
کپی کردن یک آرایه
var shallowCopy = fruits.slice(); // this is how to make a copy
// ["Strawberry", "Mango"]
Syntax
[element0, element1, ..., elementN] new Array(element0, element1[, ...[, elementN]]) new Array(arrayLength)
Parameters
elementN
- A JavaScript array is initialized with the given elements, except in the case where a single argument is passed to the
Array
constructor and that argument is a number (see the arrayLength parameter below). Note that this special case only applies to JavaScript arrays created with theArray
constructor, not array literals created with the bracket syntax. arrayLength
- If the only argument passed to the
Array
constructor is an integer between 0 and 232-1 (inclusive), this returns a new JavaScript array with itslength
property set to that number (Note: this implies an array ofarrayLength
empty slots, not slots with actualundefined
values). If the argument is any other number, aRangeError
exception is thrown.
Description
Arrays are list-like objects whose prototype has methods to perform traversal and mutation operations. Neither the length of a JavaScript array nor the types of its elements are fixed. Since an array's length can change at any time, and data can be stored at non-contiguous locations in the array, JavaScript arrays are not guaranteed to be dense; this depends on how the programmer chooses to use them. In general, these are convenient characteristics; but if these features are not desirable for your particular use, you might consider using typed arrays.
Arrays cannot use strings as element indexes (as in an associative array) but must use integers. Setting or accessing via non-integers using bracket notation (or dot notation) will not set or retrieve an element from the array list itself, but will set or access a variable associated with that array's object property collection. The array's object properties and list of array elements are separate, and the array's traversal and mutation operations cannot be applied to these named properties.
Accessing array elements
JavaScript arrays are zero-indexed: the first element of an array is at index 0
, and the last element is at the index equal to the value of the array's length
(en-US) property minus 1. Using an invalid index number returns undefined
.
var arr = ['this is the first element', 'this is the second element', 'this is the last element'];
console.log(arr[0]); // logs 'this is the first element'
console.log(arr[1]); // logs 'this is the second element'
console.log(arr[arr.length - 1]); // logs 'this is the last element'
Array elements are object properties in the same way that toString
is a property, but trying to access an element of an array as follows throws a syntax error because the property name is not valid:
console.log(arr.0); // a syntax error
There is nothing special about JavaScript arrays and the properties that cause this. JavaScript properties that begin with a digit cannot be referenced with dot notation; and must be accessed using bracket notation. For example, if you had an object with a property named '3d'
, it can only be referenced using bracket notation. E.g.:
var years = [1950, 1960, 1970, 1980, 1990, 2000, 2010];
console.log(years.0); // a syntax error
console.log(years[0]); // works properly
renderer.3d.setTexture(model, 'character.png'); // a syntax error
renderer['3d'].setTexture(model, 'character.png'); // works properly
Note that in the 3d
example, '3d'
had to be quoted. It's possible to quote the JavaScript array indexes as well (e.g., years['2']
instead of years[2]
), although it's not necessary. The 2 in years[2]
is coerced into a string by the JavaScript engine through an implicit toString
conversion. It is, for this reason, that '2'
and '02'
would refer to two different slots on the years
object and the following example could be true
:
console.log(years['2'] != years['02']);
Similarly, object properties which happen to be reserved words(!) can only be accessed as string literals in bracket notation (but it can be accessed by dot notation in firefox 40.0a2 at least):
var promise = {
'var' : 'text',
'array': [1, 2, 3, 4]
};
console.log(promise['var']);
Relationship between length
and numerical properties
A JavaScript array's length
(en-US) property and numerical properties are connected. Several of the built-in array methods (e.g., join()
(en-US), slice()
(en-US), indexOf()
(en-US), etc.) take into account the value of an array's length
(en-US) property when they're called. Other methods (e.g., push()
(en-US), splice()
(en-US), etc.) also result in updates to an array's length
(en-US) property.
var fruits = [];
fruits.push('banana', 'apple', 'peach');
console.log(fruits.length); // 3
When setting a property on a JavaScript array when the property is a valid array index and that index is outside the current bounds of the array, the engine will update the array's length
(en-US) property accordingly:
fruits[5] = 'mango';
console.log(fruits[5]); // 'mango'
console.log(Object.keys(fruits)); // ['0', '1', '2', '5']
console.log(fruits.length); // 6
Increasing the length
(en-US).
fruits.length = 10;
console.log(Object.keys(fruits)); // ['0', '1', '2', '5']
console.log(fruits.length); // 10
Decreasing the length
(en-US) property does, however, delete elements.
fruits.length = 2;
console.log(Object.keys(fruits)); // ['0', '1']
console.log(fruits.length); // 2
This is explained further on the Array.length
(en-US) page.
Creating an array using the result of a match
The result of a match between a regular expression and a string can create a JavaScript array. This array has properties and elements which provide information about the match. Such an array is returned by RegExp.exec
(en-US), String.match
(en-US), and String.replace
(en-US). To help explain these properties and elements, look at the following example and then refer to the table below:
// Match one d followed by one or more b's followed by one d
// Remember matched b's and the following d
// Ignore case
var myRe = /d(b+)(d)/i;
var myArray = myRe.exec('cdbBdbsbz');
The properties and elements returned from this match are as follows:
Property/Element | Description | Example |
input |
A read-only property that reflects the original string against which the regular expression was matched. | cdbBdbsbz |
index |
A read-only property that is the zero-based index of the match in the string. | 1 |
[0] |
A read-only element that specifies the last matched characters. | dbBd |
[1], ...[n] |
Read-only elements that specify the parenthesized substring matches, if included in the regular expression. The number of possible parenthesized substrings is unlimited. | [1]: bB [2]: d |
Properties
Array.length
- The
Array
constructor's length property whose value is 1. get Array[@@species]
(en-US)- The constructor function that is used to create derived objects.
Array.prototype
- Allows the addition of properties to all array objects.
Methods
Array.from()
(en-US)- Creates a new
Array
instance from an array-like or iterable object. Array.isArray()
(en-US)- Returns true if a variable is an array, if not false.
Array.of()
- Creates a new
Array
instance with a variable number of arguments, regardless of number or type of the arguments.
Array
instances
All Array
instances inherit from Array.prototype
. The prototype object of the Array
constructor can be modified to affect all Array
instances.
Properties
Methods
Mutator methods
Accessor methods
Iteration methods
Array
generic methods
Array generics are non-standard, deprecated and will get removed in the near future.
Obsolete since Gecko 71 (Firefox 71 / Thunderbird 71 / SeaMonkey 2.68)
This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.
Sometimes you would like to apply array methods to strings or other array-like objects (such as function arguments (en-US)). By doing this, you treat a string as an array of characters (or otherwise treat a non-array as an array). For example, in order to check that every character in the variable str is a letter, you would write:
function isLetter(character) {
return character >= 'a' && character <= 'z';
}
if (Array.prototype.every.call(str, isLetter)) {
console.log("The string '" + str + "' contains only letters!");
}
This notation is rather wasteful and JavaScript 1.6 introduced a generic shorthand:
if (Array.every(str, isLetter)) {
console.log("The string '" + str + "' contains only letters!");
}
Generics (en-US) are also available on String
.
These are not part of ECMAScript standards and they are not supported by non-Gecko browsers. As a standard alternative, you can convert your object to a proper array using Array.from()
(en-US); although that method may not be supported in old browsers:
if (Array.from(str).every(isLetter)) {
console.log("The string '" + str + "' contains only letters!");
}
Examples
Creating an array
The following example creates an array, msgArray
, with a length of 0, then assigns values to msgArray[0]
and msgArray[99]
, changing the length of the array to 100.
var msgArray = [];
msgArray[0] = 'Hello';
msgArray[99] = 'world';
if (msgArray.length === 100) {
console.log('The length is 100.');
}
Creating a two-dimensional array
The following creates a chess board as a two-dimensional array of strings. The first move is made by copying the 'p' in (6,4) to (4,4). The old position (6,4) is made blank.
var board = [
['R','N','B','Q','K','B','N','R'],
['P','P','P','P','P','P','P','P'],
[' ',' ',' ',' ',' ',' ',' ',' '],
[' ',' ',' ',' ',' ',' ',' ',' '],
[' ',' ',' ',' ',' ',' ',' ',' '],
[' ',' ',' ',' ',' ',' ',' ',' '],
['p','p','p','p','p','p','p','p'],
['r','n','b','q','k','b','n','r'] ];
console.log(board.join('\n') + '\n\n');
// Move King's Pawn forward 2
board[4][4] = board[6][4];
board[6][4] = ' ';
console.log(board.join('\n'));
Here is the output:
R,N,B,Q,K,B,N,R P,P,P,P,P,P,P,P , , , , , , , , , , , , , , , , , , , , , , , , , , , , p,p,p,p,p,p,p,p r,n,b,q,k,b,n,r R,N,B,Q,K,B,N,R P,P,P,P,P,P,P,P , , , , , , , , , , , , , , , , , ,p, , , , , , , , , , p,p,p,p, ,p,p,p r,n,b,q,k,b,n,r
Using an array to tabulate a set of values
values = [];
for (var x = 0; x < 10; x++){
values.push([
2 ** x,
2 * x ** 2
])
};
console.table(values)
Results in
0 1 0 1 2 2 2 4 8 3 8 18 4 16 32 5 32 50 6 64 72 7 128 98 8 256 128 9 512 162
(First column is the (index))
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 1st Edition (ECMA-262) | Standard | Initial definition. |
ECMAScript 5.1 (ECMA-262) The definition of 'Array' in that specification. |
Standard | New methods added: Array.isArray (en-US), indexOf (en-US), lastIndexOf (en-US), every (en-US), some (en-US), forEach (en-US), map (en-US), filter (en-US), reduce , reduceRight (en-US) |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Array' in that specification. |
Standard | New methods added: Array.from (en-US), Array.of , find (en-US), findIndex (en-US), fill (en-US), copyWithin (en-US) |
ECMAScript 2016 (ECMA-262) The definition of 'Array' in that specification. |
Standard | New method added: Array.prototype.includes() (en-US) |
ECMAScript (ECMA-262) The definition of 'Array' in that specification. |
Living Standard |
Browser compatibility
BCD tables only load in the browser